We have developed a novel diagnostic method to detect single point mutations in transcribed genes which is based on the ability of RNAseA to recognize and cleave single base mismatches in RNA:RNA heteroduplexes, and we have applied this method to analyze the involvement of ras mutational activation in human tumorigenesis. Our data support the concept that ras oncogenes are contributing in a dominant but dose-dependent manner to the process of tumor development and progression and for the first time demonstrate the frequent involvement of somatic ras mutational activation in the early stages of human tumorigenesis. We propose in this application to continue these studies to resolve a series of issues raised by our previous findings concerning the role that mutant ras oncognees are playing in human tumorigenesis. The experimental strategy will involve a screening descriptive approach by utilization of combinations of molecular genetics diagnostic techniques to detect, characterize and estimate the relative expression level of mutant ras oncogenes in human tumors at different stages of progression, and a functional approach using animal tumorigenicity and metastasis model systems. Emphasis will be made in the analysis of human colon carcinomatogenesis, inluding benign adenomatous polyps and villous adenomas. Clinical follow-up studies will be performed in an effort to determine whether apparent corelations previously found between various aspects of the nature and expression levels of the c-K-ras onogene and the histopathological charateristics of the corresponding colon tumors could have a prognostic value for this common type of human cancer. Successful development of these studies would have direct applications for diagnosis and prognosis in human cancer and should yield useful information at the molecular genetic level on the role of oncogene activation in various basic aspects of tumor biology such as the metastatic process and the heterogeneity of solid tumors.